Enclosed Space Entry: Safe Procedure & Permit to Work

The fatal hazards of confined spaces, gas testing to 21% oxygen, and the permit, standby and rescue rules that keep crews alive.

8 min read

Intermediate

Ship Construction & Naval Architecture

Key Principles at a Glance 6 points

A risk assessment for enclosed space entry is carried out by the Second Engineer or Chief Officer, with a meeting to discuss possible hazards and a clear list of the work to be done, including rescue operations.
Always assume toxic gas may be present, open and secure the space cover with precaution, and check whether the space is pressurised before entry.
All fire hazards must be minimised before hot work, for example by emptying fuel or chemical tanks nearby, and the space must be well ventilated.
The space must be tested for sufficient oxygen and other gases: the oxygen level should be 21% by volume, and anything less is not acceptable and requires more ventilation.
A permit to work must be filled out and checked, is valid only for a certain time period, and must be authorised by the Master; signs and "men at work" boards prevent others from starting machinery or operations.
One person must always be kept on standby, the entrant should carry a lifeline and a continuously operating oxygen analyser, and rescue/resuscitation equipment and means of hoisting an incapacitated person must be available outside.

1. The Enclosed Space & Its Fatal Hazards

An enclosed space is any confined compartment — cargo hold, ballast tank, fuel tank, cofferdam, void space, duct keel, chain locker, or pump room — where the atmosphere cannot be assumed safe. These spaces kill quickly and quietly, which is why a strict procedure is mandatory before entry.

Primary Hazards:

Oxygen deficiency: Rusting, cargo, or inert gas can consume oxygen. The oxygen level must be 21% by volume; anything less is not acceptable.
Toxic gases: Hydrogen sulphide, carbon monoxide, and hydrocarbon vapours can be present even when there is no smell.
Flammable atmosphere: Hydrocarbon vapours within the flammable range can ignite from a spark or hot work.
Physical hazards: Slippery surfaces, falls from height, moving machinery, and engulfment.

The Golden Rule

Assume about toxic gas being present. Never rely on smell or on a space having been entered safely before. Test the atmosphere, ventilate, and follow the permit system every single time.

Figure 1: Enclosed Space Hazards. Confined compartments accumulate deadly toxic gas, flammable cargo vapours, and suffer severe oxygen deficiency due to steel corrosion. The atmosphere must be tested and confirmed safe before any entry.

2. Risk Assessment & Pre-Entry Preparation

Before any enclosed space entry, a formal risk assessment and preparation process must be completed:

Risk assessment carried out by the Second Engineer (2/E) or Chief Officer (C/O).
A meeting discussing the possible hazardous situation.
A list of the work to be done is made, so the work can be carried out easily and quickly.
The risk assessment includes the rescue operation to be performed, etc.
Assume toxic gas is present.
Open and secure the enclosed space cover with precaution — and check whether the space is pressurised or not.
All fire hazards must be minimised if hot work is to be carried out. This can be done by emptying fuel or chemical tanks nearby the hot work.
The space must be well ventilated.
The space must be checked for sufficient oxygen and other gases.
Enough lighting and illumination should be present before entering.

Figure 2: Pre-Entry Preparation. Risk assessment by the 2/E or C/O, hazard meeting, work & rescue plan, positive mechanical isolation, forced ventilation, gas testing, intrinsically safe lighting, and formal Master authorization.

3. Atmosphere Testing & The Permit to Work

Atmosphere Testing:

The space should be checked for sufficient O2 level and for other gases.
The O2 level should be 21% by volume. A percentage less than that is not acceptable, and more time for ventilation should be given in such circumstances.
Enough lighting and illumination should be present in the enclosed space before entering.

The Permit to Work:

A proper permit to work has to be filled out and a checklist checked so as to prevent any accident which can endanger life.
The permit is to be valid only for a certain time period. If the time period expires, then a new permit must be issued and the checklist filled out again.
The permit has to be checked and permitted by the Master in order to work in a confined space.
Proper signs and "Men at Work" sign boards should be provided so that no one starts any equipment, machinery or operation in the confined space, endangering the life of the people working.
The Duty Officer has to be informed before entering the enclosed space.
The checklist has to be signed by the person involved in the entry and also by a competent officer.

Figure 3: Atmosphere Testing & Permit to Work. Space tested at top, middle, and bottom using calibrated multi-gas equipment (O₂ 20.9%, LEL <1%, CO <25 ppm, H₂S <5 ppm). The permit is strictly time-limited and formally authorized by the Master.

4. Entry Protocol, Standby Man & Rescue

Once the preparation and permit are complete, the entry itself follows strict rules:

One person must always be kept on standby to communicate with the person inside the space.
The person may carry a lifeline with them inside.
The person should carry an oxygen analyser inside the enclosed space, and it should be on all the time to monitor the oxygen content.
As soon as the level drops, the analyser should sound an alarm and the space should be evacuated quickly without delay.
No source of ignition is to be taken inside unless the Master or competent officer is satisfied.
The number of persons entering should be limited to those actually needed inside for the work.
Rescue and resuscitation equipment must be present outside the confined space. Rescue equipment includes breathing air apparatus and spare charge bottles.
Means of hoisting an incapacitated person should be available.
After finishing the work, when the person is out of the enclosed space, the after-work checklist has to be filled and the permit to work closed.

Cargo Pump-Room Safety — Four Numbers (Solved Q25):

Tanker pump rooms concentrate every cargo pipeline in one space, so the paper treats them as the worked example of the whole entry chapter. Recite it as air — spark — watch — light:

Air — 20 changes/hour: mechanically ventilated at 20 air changes per hour of the room volume; vent outlets at least 3 m horizontally from any ignition source and from the nearest accommodation or service opening.
Spark — permit + multi-gas: entry only on the enclosed-space entry permit with the Master's permission; carry a multi-gas personnel detector — any warning means evacuate immediately.
Watch — alarm in control: a continuous audible and visual alarm sounds automatically in the cargo control room or pump control station.
Light — interlocked: lighting (except emergency lighting) is interlocked with ventilation — ventilation must be running to switch lights on, but lights stay on if ventilation fails.

Never Become a Second Casualty

Most enclosed-space fatalities are would-be rescuers who entered without protection. If the entrant collapses, do not rush in — raise the alarm, don the breathing apparatus, and use the lifeline and hoisting equipment from outside.

Figure 4: Entry Team & Rescue. A standby attendant remains stationed outside with communications, entrant carries a personal continuous gas analyser, and tripod hoist, SCBA sets, resuscitator and stretcher are fully rigged before entry.